Automatic transistor bar etching



Spt -13, 1960 B. coRNELlsoN AUTOMATIC TRANSISTOR' BAR ETCHING Filed001'.. l1, 1956 INVENTOR qyd 'amelisolv Wm www ATTORNEYS crystal into?.asplurality of transistor bars.

United States Patent G 2,952,528 v AU'roMArtc 'mANsIsronAR ETCHING BoydlCornelison, Dallas, Tex., assignor to Texas Instruments Incorporated,Dallas, Tex., a corporation of Delaware Filed Oct. 11, 195'6, Ser. No.615,285

4 Claims. (Cl. 4l-'42) terial properly doped by some suitable means,as'for' example, in a crystal puller, and thereafter cutting the n Thecutting operationsarenormally conducted by sawing with diamondstudded'blades or by a cavitron. As a result of 'these operations thesurface region of each bar is distributed due to shocks and other.harmful disturbances and this surface""region must be removed by some.convenient means'prior to thecomp'le'tion of transistors employing thebars. The most convenient means is to etch fthe bars. In etching, as itis done today, the transistor bars are simply dumped into an etchingsolution where they are allowed to remain until upon visual observationit appears that a suflicient portion of the surface of each bar has beenremoved. Thereafter, the bars are removed from the solution, washed anddried, and are sized. After sizing they are then ready for mounting.

Although the preceding paragraph refers specifically to transistor bars,it is to be understood that the invention broadly relates to all typesand forms of bars of any material whatever.

It is an object of the present invention to provide a method whereby theetching of bars and transistor bars in particular can be conducted in acontinuous fashion without the necessity of continually observing theetching process in order to insure that the bars are not etched -tooseverely. In addition to the etching, the bars are sized, therebyrelieving the necessity to pursue this operation as a separate step.Essentially, this is achieved by placing the bars to be treated in anetching solution and by supporting the bars in a unique fashion so thatwhen the bars have been reduced in size by virtue of the etching action,they will be able to pass through the bar support and will gravitate outof the etching solution into an inert medium which will stop furtheretching action. As will be evident, this procedure results in the barsbeing both etched and sized at the same time. As a refinement to themethod and app-aratus of the invention, the bars are further removedfrom the inert medium and led to a collector receptacle ready to betaken to lthe next step in their handling.

By the present invention, there is provided for the first time a methodfor automatically conducting an etching process with reference totransistor bars that also sizes them, thereby avoiding a separate stepfor this purpose. The method is characterized by simplicity andreliability plurality of -slots each having a etching solution into thisarea. municates the space within, the depending skirt 14 above,

and the invention can be carried out quite economically and expediently.

Other and further objects of the present invention will become apparentfrom the following detailed description of a preferred embodiment of theinvention when taken in conjunction with the drawings in which:

Figure 1 shows the apparatus employed to carry out the method of thepresent invention; and

Figure 2 is a view in section of Figure 1 taken along line 2-2.

Referring now to the drawing in detail, a preferred embodiment of theapparatus of the present invention will be described. There is provideda container 10 having a sloping bottom 11, which is substantiallyconical in design, having a discharge spout 12 located at the lowernrostpoint of the sloping bottom 11. In addition, the container 10 isprovided with a top annular cover 13 having a central depending skirt1'4 which projects inwardly of the container 10. Positioned within thedepending skirt 14 and supported thereby is a bar support 15 in the formof a grid. The support 15 defines a parallel troughs each defining anopen bot-` tom. 'I'he troughs are defined by adjacent tom of each troughis designated by the numeral 17. In

effect the support or grid 15 defines a series of parallel width equaltothe desired width of a bar at the conclusion of a normal etchingoperation. A pipe 20 is provided emptying into the space defined withinthe depending skirt 14 for the` purpose of introducing A drain pipe 21comthe grid 15 with a point outside of the container 10 and functions asan overflow pine.

In the practice of the invention, an inert medium is placedin thecontainer 10 as indicated by the numeral 25. This inert medium may beany composition which Will stop the etching action of an etching fluidon a bar. Examples of inert fluid which can be used are carbontetrachloride (C014), compositions made -by the Minnesota Mining andManufacturing Company, and designated by the trade names Fluorochemical(ll-75, which is a completely fluorinated cyclic ether with theempirical formula CaFmO and Fluorochernical N-43 which isheptacosafluorotributylamine expressed empirically as (C4F9)3N, andAroclor-l248, a material produced by the Monsanto Chemical Company;Aroclor being a trade name of a series of polychlorinated polyphenyls,of which No. V1248 is particularly adapted for use in the instantinvention. Although several specific examples for inert fluid 25 havebeen given, it will be understood that there are other substances andcompounds which will be useful as inert duid 25 includingfluoro-chemicals other than those named above. Specific mention is meantto' be by Way of illustration and not limitation. The inert fluid 25 isplaced in the the level indicated by the numeral 26 which, as will beapparent, is above the lower end of the depending skirt 14. At the sametime etching fluid is introduced through the pipe 20 within thedepending skirt 1'4 By the proper choice of specific gravity, theetching fluid will rest on top of the inert medium in the space withinthe depending skirt 14. The interface between the etching fluiddesignated by the numeral 27 and the inert medium 25 within thedepending skirt 14 is referenced by the numeral 28. It will be apparentthat the lower level of the etching fluid will be below the bar support15, but above the lower end of the depending skirt 14. It will also beapparent Ithat the etching fluid is immiscble 'With reference to theinert medium and is of lesser specific gravity.

Bars are introduced onto the bar support 15 through the opening definedby the annular cover "13 and by the angle sections container 10 up to`very construction of the bar support 15, the bars will assume apositionin alignment with the troughs dened by the bar support 15. Since thebars designated by the numeral 30 .are in the-etching medium at thistime, they will be attacked and gradually reducedfin width. When thebars have been eaten yaway to a width about equal to the-width of theslots '17, they will then pass through the bar support 1'5, fall throughthe inert medium Z5, as Iis Vindic-:ated bythe bar Y31,1 fall throughthe spout 12, las indicated Vby thebar 32, and .onto an endless beltconveyor '33 which will'carry 'them to a collector receptacle Y34. Theendless'belt conveyor 33 is designed as a mesh or screen and uid passingthrough the spout 12 will pass through the endless belt 33 and bereceived in a receptacle 35. A pump i36 `draws the inert iluid from thereceptacle 35 via ,conduit 37 -and recirculates it via conduit 3Sbackinto the container 10. It will be. appreciated that the pump 36 willoperate at a volume ratesufficient to return inert uid to the containerat substantially the same volume rate as the inert fluid is leaving thecontainer 10 vthrough the spout 12.

ATransistor bars Amust'be sized .in one manner or another prior tomounting them in Yheaders or otherwise. Since the etching is allowedtorproceed until the bars can pass through the bar support, theyareautomatically sized. Thus, this technique does both the etching andsizing asone step avoidingextra'steps and achieving better and moreVstandardized results than if the etching and sizing were doneseparately.

Although lthe invention has been shown and described with reference to apreferred form of the invention, nevertheless, various changes andmodifications obvious to one skilled inthe art are deemed tobe Withinthe spirit,tscope and contemplation of the invention.

What is claimed is: Y 1 Y 1. Method of etching comprising introducing anarticle to be etched into an etching hmedium supported on an 4 Yimmiscible inert medium, at the adjacent interface of th two media,supporting said article in said etching medium, releasing said articleresponsive to a predetermined reduction in size and transferring saidarticle through said interface to said inert medium to stop furtheretching action. Y ,Y

2. Method of etching comprising introducing an article to be etched intoan etching medium supported on an immiscible inert medium, attheadjacent inter-face of the two m'edia, -supportings'aid article insaidfetching medium, releasing said article responsive Lto -a'predetermined reduction in size to fall through said interface bygravity into said inert .medium to stop further etching action. A i Y 3.Method of etching-comprising introducing an article to be etched into anetching solution supported on an imrniscible inert heavier solution,supporting said article in said etching solution, releasing said articleresponsive to a predetermined reduction in size to fall into saidinertsolution to stop further etching action and transferring said article toa point of collection.

`4. Method of etching comprisingiritro'ducingran 'article l to be etchedinto an etching mediurnoating in a captive condition on an immiscibleinert medium, 's'uppor'ting said article in said etching medium,releasing said article responsive to a predetermined reduction in sizeto fallfbyf gravity into -said inert medium `to stop further etchingaction, @discharging said article from said inert medium4 and receiving`said discharged article and conveying same to a collectionpoint'.

References Cited in Vthe tile 'of this 'patent y UNITED STATES PATENTS

1. METHOD OF ETCHING COMPRISING INTRODUCING AN ARTICLE TO BE ETCHED INTOAN ETCHING MEDIUM SUPPORTED ON AN IMMISCIBLE INERT MEDIUM, AT THEADJACENT INTERFACE OF THE TWO MEDIA, SUPPORTING SAID ARTICLE IN SAIDETCHING MEDIUM, RELEASING SAID ARTICLE RESPONSIVE TO A PREDETERMINED RE-